In the drilling of wells the recovery of liquids from the bottom of the well is usually achieved by either the use of pressure to push the liquid to the well head or by pumping the liquid to the well head. When pumping is utilized the pump itself is lowered down into the well below the liquid level. The motors for driving the pumps can be either located near the well surface or can themselves be lowered into the liquid at the bottom of the well hole. If the pump-driving motors are submerged into the liquid, as is most commonly done, problems of motor corrosion can become acute. This is especially true for those wells which contain corrosive materials such as H.sub.2 S.
The submersible pump motors are generally filled with lubricating fluid and have construction for providing protection against seepage of the corrosive well liquid into the motor interior. Some protection against seepage is obtained by the use of mechanical seals. Unfortunately, such seals are not a panacea for the seepage problems and motor failure will still occur. This is due in part to the change in volume of the luricating liquid in the motor as motor temperatures rise and fall. When the motor temperature rises, because of motor friction and high well temperatures, the volume of the lubricating liquid increases which causes seepage of the liquid out through the motor seals into the well itself. At this point entrance of corrosive well fluids into the interior of the motor is not large. However, when the motor temperature falls, the lubricating liquid volume decreases causing a "suction" which pulls corrosive well fluids through the motor seals into the motor. When this occurs, in wells containing H.sub.2 S for example, the sulfide will readily emulsify or dissolve into the lubricating liquid and contact the copper motor windings resulting in corrosion of the windings. As the windings become badly corroded the motor "shorts out" therefore terminating motor life.
Rubber or synthetic rubber-like diaphrams attached to the motor housing have been used to compensate for expansion and contraction of the lubricating liquid to provide seal protection. However the use of such diaphrams is not an entirely satisfactory solution in wells which operate at high temperatures or which contain hydrocarbons as these diaphrams tend to deteriorate under such conditions and fail. Failure of the diaphrams results in a flooding of the electric motor with corrosive material and destruction of the motor.
Attempts at providing protection against seepage have also been made by providing an interface between the lubricating liquid and the well liquid in a chamber remote from the motor interior. By maintaining such an interface, contact between corrosive materials in the well liquid and the motor interior will be prevented provided the corrosive material is not soluble in the lubricating liquid. If there is solubility of corrosive material, as is the case with H.sub.2 S, maintenance of the interface is of little value for insuring long motor life.
Therefore it is an object of this invention to provide an apparatus which protects and isolates submersible electric motors from corrosion over a wide range of well conditions.